I constantly use it to boost solo volume then again tone down my right hand while I sing.
I use it much in the same way on my Tyros 2. Also some voices seem to be louder or softer than others so I need to constantly adjust.
On my KMA I feel like I can get by just fine without a volume pedal because it has dedicated sliders that adjust the style or RH voice volume. I guess if I had an organ background I'd still need to use the volume pedal though.